The objective of the proposed investigation is a more thorough understanding of the structure and function of the eukaryotic chromosome. The giant polytene chromosomes of Drosophila will be employed as a model system to explore features of chromosomes that are common to all higher organisms. Three independent approaches will be taken: 1. Through studies of a specific deoxyribonuclease we intend to: a. establish more firmly the significance of chromosomal puffing by demonstrating that one puff is responsible for the production of a specific cellular enzyme. b. explore the mechanism of gene activation by investigating the induction of this enzyme at the cytological and biochemical levels. 2. Through studies of bromodeoxyuridine (BUdR) incorporation into polytene chromosomes we intend to: a. determine whether a specific inhibitor of the expression of new gene activity (BUdR) acts at the level of transcription. b. determine if BUdR has an all-or-none effect on transcription in polytene chromosomes. c. determine if BUdR can be used as a tool to study the specific interaction of homologous chromosomes. 3. Through molecular hybridization studies: a. we will study the homology between salivary- gland RNA and unique DNA sequences with RNA excess experiments. b. we will attempt to isolate and characterize the primary transcription product of a specific gene.